1. Field of the Invention
This invention concerns corrosion inhibitors, and more particularly to specific carboxylic acid/salt combinations which inhibit corrosion in heat transfer fluids, such as antifreezes.
2. Description of Related Invention
Metallic materials used in heat-transfer systems, such as internal combustion engines, undergo corrosive attack from heat transfer fluids, such as aqueous media containing antifreeze. The resulting metal damage, such as pitting and metal loss, causes perforations or other defects leading to fluid loss and system failure.
Various corrosion inhibitors have been added to heat transfer fluids to reduce corrosion of metallic systems. For example, U.S. Pat. No. 4,587,028 (Darden) discloses non-silicate antifreeze formulations containing alkali metal salts of benzoic acid, dicarboxylic acid and nitrate. Additional ingredients including alkali metal hydroxides, alkali metal nitrates and aromatic triazoles, such as tolyltriazole or benzotriazole are preferably provided. U.S. Pat. No. 4,647,392 (Darden et al.) discloses corrosion inhibitors using aliphatic monobasic acids or salts, hydrocarbyl dibasic acids or salts and hydrocarbonyl triazole. U.S. Pat. No. 4,657,689 (Darden) discloses corrosion inhibitors containing aliphatic monobasic acids or salts, hydrocarbyl dibasic acids or salts, hydrocarbyl azoles and specific hydrocarbyl alkali metal sulfonates. U.S. Pat. No. 5,085,791 (Burns) discloses antifreeze compositions containing cyclohexane acid corrosion inhibitor alone or in combination with other corrosion inhibitors, particularly sebacic acid and tolyltriazole. The cyclohexane acid includes cyclohexyl carboxylic (formic) acid, cyclohexyl acetic acid and cyclohexyl propionic acid. The cyclohexane acid is targeted to inhibit lead solder and/or aluminum corrosion. U.S. Pat. No. 4,105,405 (Wehle et al.) discloses the use of cyclohexane hexacarboxylic acid corrosion inhibitors.
These and other combinations of corrosion inhibitors generally use azoles and/or other compounds either as essential or preferred components. Azoles are generally used to inhibit copper and brass corrosion and to assist in the protection of iron and steel. Other typical corrosion inhibitors include silicates, phosphates, nitrates and other commonly used materials. Many corrosion inhibitors, however, have limited utility. For example, silicates can cause gelling leading to system damage or seal wear, requiring the addition of stabilizers. Azoles, like tolyltriazole, deplete from the system relatively rapidly requiring the expense of replacement and disposal problems. The presence of amines can lead to formation of nitrosamines which are carcinogens creating disposal problems. These and other difficulties of many corrosion inhibitors limit the utility of current, commercial corrosion inhibitors.
Corrosion inhibitors are needed which are effective in inhibiting corrosion in a wide variety of metals and which have long term stability without the addition of stabilizers and without other harmful or limiting properties.